WO 2008/131735 A1 discloses a light emitting diode chip wherein a first and second electrical connection layer are arranged at a rear side of the light emitting diode chip situated opposite the radiation exit area and are electrically insulated from one another by a separating layer, wherein a partial region of the second electrical connection layer extends from the rear side through a perforation of the active layer in the direction toward the front side of the light emitting diode chip. Making contact with a semiconductor chip in this way has the advantage that the radiation exit area can be free of contact areas and, consequently, the emitted radiation is not shaded.
The light emitting diode chip is a so-called “thin-film” light emitting diode chip, wherein the original growth substrate of the semiconductor layer sequence is detached and, instead, the semiconductor layer sequence connects to a carrier by a solder layer at an opposite side relative to the original growth substrate. In the case of a thin-film light emitting diode chip of this type, it is advantageous if that side of the semiconductor layer sequence facing the carrier is provided with a mirror layer to deflect radiation emitted in the direction of the carrier in the direction of the radiation exit area and thereby to increase radiation efficiency.
For the visible spectral range, silver, in particular, is suitable as a material for the mirror layer. Silver is distinguished by a high reflection in the visible spectral range and produces a good electrical contact to the semiconductor material. On the other hand, however, silver is susceptible to corrosion and migration of the silver into adjacent layers can occur.
To protect a mirror layer composed of silver against corrosion, generally a protective layer is applied to the silver layer. By way of example, a platinum layer is suitable as a protective layer. However, it has been found that the platinum can penetrate into the silver layer at the process temperatures customary for applying the layers and can even pass as far as the opposite interface between the mirror layer and the semiconductor layer. The reflection of the interface between the mirror layer and the semiconductor layer sequence can be impaired as a result. This has the consequence that the light coupling-out and thus the efficiency of the light emitting diode chip are reduced. Furthermore, the electrical properties can also change as a result of the diffusion of platinum to the interface between the semiconductor layer sequence and the mirror layer.
It could therefore be helpful to provide a light emitting diode chip comprising a rear-side mirror layer protected against corrosion by a protective layer, wherein the reflection and electrical properties of the interface between the silver layer and the semiconductor layer sequence are not impaired.